<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
       div {
           width: 300px;
           background-color: rgba(102,102,102,0.3);
           padding: 10px;
           position: relative;
       }
       input {
           width: 300px;
           text-decoration: none;
           border: 0;
           box-sizing: border-box;
           padding: 10px 20px;
       }
       img {
           position: absolute;
           right: 20px;
           top: 14px;
       }
       p {
           font-size: 12px;
           color: red;
           margin: 0px;
       }
    </style>
</head>
<body>
    <div>
        <input type="text" placeholder="请输入用户名" >
        <img src="http://doc.vrd.net.cn/tstore_v1/images/login/yhm.png" alt="">
        <p>用户名不能为空</p>
    </div>
</body>
</html>